1. Field of the Invention:
The present invention relates to a high definition television (HDTV) receiver capable of displaying both a current standard color television signal (NTSC, PAL, SECAM etc.) and a high definition television signal having a horizontal deflection frequency about twice that of the current standard color television signal. Particularly, the present invention is intended to provide an HDTV receiver including a double speed processing portion for processing the current standard color television signal at a double speed, a circuit arrangement and construction of which are improved such that the HDTV receiver becomes compact and low cost and can prevent an image quality from being degraded when a double speed conversion is performed for the current standard color television signal.
In this description, the NTSC system will be described as a typical example of the current standard color television system.
2. Description of Prior Art:
Recently, programs of HDTV System, called "Hi-Vision" system in Japan, and of ADTV (Advanced Television) system, called "Clearvision" in Japan, are distributed through a broadcasting or in a packaged media and becoming popular. Compared to current TV broadcasting systems such as the NTSC system, the HDTV or ADTV system presents much higher picture quality. Among those high picture quality broadcasts, the MUSE system belongs to the HDTV system and the first and second generation Extended Television (EDTV) systems belong to the ADTV system.
Vertical deflection frequencies of the Hi-Vision system, the Clearvision system and the NTSC system are substantially the same. However, the horizontal deflection frequency of the Hi-Vision system as well as the Clearvision system is about twice that of the NTSC system. That is, the number of scanning lines of the Hi-Vision system or the Clearvision system is about twice that of the NTSC system. An NTSC signal processing in a HDTV receiver capable of displaying both the HDTV signal and the NTSC signal is performed according to one of the following three systems:
(1) Clearvision system,
(2) Double speed field processing system,
(3) Horizontal deflection frequency switching system.
The difference between these three signal processing systems and the HDTV signal configuration are shown in the Table which will follow and FIGS. 5(a) to 5(c).
As shown in FIG. 5(c), the Clearvision system is a double density, non-interlace system and scanning line signals 1' and 2' are generated by interpolation. That is, the scanning line signals 1' and 2' are generated by adaptively
TABLE __________________________________________________________________________ DOUBLE SPEED HORIZONTAL FIELD PROCESS DEF. FREQUENCY CLEARVISION SYSTEM SYSTEM SWITCHING SYSTEM HI-VISION __________________________________________________________________________ SIGNAL fh (HORIZONTAL DEF. 31.5 31.5 15.75 33.75 FREQUENCY) [khz] fv (VERTACAL DEF. 60 120 60 60 FREQUENCY) [Hz] INTERLACE/ NON-INTERLACE INTERLACE INTERLACE INTERLACE NON-INTERLACE SIGNAL INTERPOLATION APPLIED NOT APPLIED NOT APPLIED __________________________________________________________________________
switching an operation of the HDTV receiver between an intra-field processing and an inter-field processing depending on the kind of picture detected, that is, a moving picture or a still picture.
In the double speed field processing system, horizontal and vertical scans are performed by electron beam deflected at a double speed as shown by solid lines in FIG. 5(b), respectively. Same lines in a first field are scanned twice with an interval of 1/120 seconds and a second field is interlaced and same lines thereof are scanned twice similarly.
In the horizontal deflection frequency switching system, the horizontal deflection frequency is switched to 15.75 kHz of the NTSC system to perform an interlace scanning of the normal NTSC system as shown by solid lines in FIG. 5(a).
In the Clearvision system or the double speed field processing system, the horizontal deflection frequency fh for the NTSC signal processing is 31.5 kHz which is twice the horizontal deflection frequency of the NTSC system and is close to the horizontal deflection frequency ranged from 31.5 to 33.75 kHz of the HDTV signal. Therefore, it is possible that the HDTV signal processing circuit and the NTSC signal processing circuit can commonly use a horizontal deflection circuit and a high voltage generating circuit advantageously. However, the Clearvision system requires a frame memory for producing the interpolation signals, which means an increase of cost, and there may be an unnatural movement of a picture at every switching from a moving picture to a still picture, which means a degradation of image quality.
On the other hand, the double speed field processing system requires a field memory and a switching device for switching a vertical deflection frequency between 120 Hz and 60 Hz when the signal processing system is changed between the NTSC signal processing and the Clearvision signal processing, causing an increase of cost.
The horizontal deflection frequency switching system requires a circuit for substantially switching of the horizontal deflection circuit and the high voltage generating circuit since the horizontal deflection frequency in the Clearvision signal processing is about twice that in the NTSC signal processing, which leads to increase of cost and increase of size of the receiver.